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1566 votes
9 answers

How do I list all databases and tables using psql?

When I log in with psql --username=postgres, how do I list all databases and tables? I have tried \d, d and dS+ but nothing is listed. I have created two databases and a few tables with pgAdmin III, ...
Jonas's user avatar
  • 33.3k
560 votes
5 answers

List all columns for a specified table

I'm looking for a precise piece of information in a database which I have no knowledge about. The database is on a separate machine, but I can log into it, and launch a psql command line, with ...
Stephane Rolland's user avatar
545 votes
4 answers

How do you mysqldump specific table(s)?

How can I dump a specific table or set of tables without including the rest of the db tables?
markdorison's user avatar
  • 5,585
487 votes
2 answers

What's the difference between a temp table and table variable in SQL Server?

This seems to be an area with quite a few myths and conflicting views. So what is the difference between a table variable and a local temporary table in SQL Server?
Martin Smith's user avatar
  • 85.4k
440 votes
5 answers

How do I list all schemas in PostgreSQL?

When using PostgreSQL v9.1, how do I list all of the schemas using SQL? I was expecting something along the lines of: SELECT something FROM pg_blah;
Stéphane's user avatar
  • 5,645
402 votes
4 answers

How to insert values into a table from a select query in PostgreSQL?

I have a table items (item_id serial, name varchar(10), item_group int) and a table items_ver (id serial, item_id int, name varchar(10), item_group int). Now I want to insert a row into items_ver ...
Jonas's user avatar
  • 33.3k
373 votes
12 answers

connect to PostgreSQL server: FATAL: no pg_hba.conf entry for host

I am trying to run a website sent to me but after doing so this error appeared connect to PostgreSQL server: FATAL: no pg_hba.conf entry for host "4X.XXX.XX.XXX", user "userXXX", ...
Jin's user avatar
  • 3,843
353 votes
3 answers

How can I time SQL-queries using psql?

I would like to benchmark some SQL-queries agains my PostgreSQL database. Is there any way I can time SQL-queries using psql?
Jonas's user avatar
  • 33.3k
309 votes
10 answers

List the database privileges using psql

I'm in the middle of a database server migration and I can't figure (after googling and searching here) how can I list the database privileges (or all the privileges across the server) on PostgreSQL ...
pedrosanta's user avatar
  • 3,403
303 votes
15 answers

Can MySQL reasonably perform queries on billions of rows?

I am planning on storing scans from a mass spectrometer in a MySQL database and would like to know whether storing and analyzing this amount of data is remotely feasible. I know performance varies ...
haxney's user avatar
  • 2,503
300 votes
4 answers

Why Does the Transaction Log Keep Growing or Run Out of Space?

This one seems to be a common question in most forums and all over the web, it is asked here in many formats that typically sound like this: In SQL Server - What are some reasons the transaction log ...
Mike Walsh's user avatar
  • 18.2k
297 votes
18 answers

How can I monitor the progress of an import of a large .sql file?

I am importing a 7 GB foobar.sql to restore a table in a local database. $ mysql -h localhost -u root 'my_data' < foobar.sql $ mysql --version /usr/local/mysql/bin/mysql Ver 14.12 Distrib 5.0....
qazwsx's user avatar
  • 3,457
282 votes
10 answers

What are the main differences between InnoDB and MyISAM?

What are the main differences between InnoDB and MyISAM?
ilhan's user avatar
  • 3,049
280 votes
7 answers

When should I use a unique constraint instead of a unique index?

When I want a column to have distinct values, I can either use a constraint create table t1( id int primary key, code varchar(10) unique NULL ); go or I can use a unique index create table t2( id ...
bernd_k's user avatar
  • 12.3k
257 votes
6 answers

How large should be mysql innodb_buffer_pool_size?

I have a busy database with solely InnoDB tables which is about 5GB in size. The database runs on a Debian server using SSD disks and I've set max connections = 800 which sometimes saturate and grind ...
alfish's user avatar
  • 2,974
249 votes
6 answers

Force drop db while others may be connected

I need to remove a database from a PostgreSQL DB cluster. How can I do it even if there are active connections? I need sort of a -force flag, that will drop all connections and then the DB. How can I ...
Alex's user avatar
  • 2,685
243 votes
18 answers

How do you document your databases?

I find that most of my clients are not documenting their databases at all and I find that pretty scary. To introduce some better practice, I would like to know what tools/process people are using. ...
241 votes
5 answers

'Access denied; you need (at least one of) the PROCESS privilege(s) for this operation' when trying to dump tablespaces

I am trying to backup mysql using the command mysqldump -u root -p database_name > backup.sql , but it is throwing an error: 'Access denied; you need (at least one of) the PROCESS privilege(s) ...
user avatar
232 votes
3 answers

Granting a user account permission to create databases in PostgreSQL

How do I give a user account in PostgreSQL the ability to create and drop databases? Is there a way to do this with GRANT?
GSto's user avatar
  • 2,423
219 votes
2 answers

Create a MySQL database with charset UTF-8

I'm new to MySQL and I would like to know: How can I create a database with charset utf-8 like I did in navicat? create mydatabase; ...seems to be using some kind of default charset.
user3397998's user avatar
  • 2,301
214 votes
5 answers

Granting access to all tables for a user

I'm new to Postgres and trying to migrate our MySQL databases over. In MySQL I can grant SELECT, UPDATE, INSERT, and DELETE privileges on a low privileged user and enable those grants to apply to all ...
PlaidFan's user avatar
  • 2,245
210 votes
7 answers

How can I optimize a mysqldump of a large database?

I have a symfony application with an InnoDB database that is ~2GB with 57 tables. The majority of the size of the database resides in a single table (~1.2GB). I am currently using mysqldump to ...
Patrick's user avatar
  • 4,279
208 votes
6 answers

When should a primary key be declared non-clustered?

While creating a test database for another question I asked earlier, I remembered about a Primary Key being able to be declared NONCLUSTERED When would you use a NONCLUSTERED primary key as opposed ...
Stuart Blackler's user avatar
203 votes
5 answers

How to get the name of the current database from within PostgreSQL?

Using \c <database_name> in PostgreSQL will connect to the named database. How can the name of the current database be determined? Entering: my_db> current_database(); produces: ERROR: ...
Amelio Vazquez-Reina's user avatar
203 votes
17 answers

How do I find PostgreSQL's data directory?

I forgot how I started PostgreSQL the last time (it was months ago) and I don't remember where the data directory is located. The postgres command seems to require the location of the data directory. ...
randomguy's user avatar
  • 2,171
200 votes
14 answers

SQL: SELECT All columns except some

Is there a way to SELECT all columns in a table, except specific ones? IT would be very convenient for selecting all the non-blob or non-geometric columns from a table. Something like: SELECT * -...
Adam Matan's user avatar
  • 11.8k
191 votes
7 answers

What's the difference between a CTE and a Temp Table?

What is the difference between a Common Table Expression (CTE) and a temp table? And when should I use one over the other? CTE WITH cte (Column1, Column2, Column3) AS ( SELECT Column1, Column2, ...
Rachel's user avatar
  • 8,487
177 votes
20 answers

Should developers be able to query production databases?

Should developers be given permission to query (SELECT / read only) production databases? The previous place I worked, the development team had the db_datareader role; where I work now the ...
Tom Hunter's user avatar
  • 2,169
175 votes
6 answers

Good explanation of cascade (ON DELETE/UPDATE) behavior

I don't design schemas everyday, but when I do, I try to setup cascade updates/deletes correctly to make administration easier. I understand how cascades work, but I can never remember which table is ...
Johntron's user avatar
  • 1,883
175 votes
6 answers

Guid vs INT - Which is better as a primary key?

I've being reading around reasons to use or not Guid and int. int is smaller, faster, easy to remember, keeps a chronological sequence. And as for Guid, the only advantage I found is that it is ...
BrunoLM's user avatar
  • 3,513
173 votes
13 answers

Should binary files be stored in the database?

What is the best place for storing binary files that are related to data in your database? Should you: Store in the database with a blob Store on the filesystem with a link in the database Store in ...
Jack Douglas's user avatar
  • 40.1k
172 votes
4 answers

Help installing SQL Server 2017 - VS Shell installation has failed with exit code 1638

Any suggestions on how to deal with this error: TITLE: Microsoft SQL Server 2017 Setup ------------------------------ The following error has occurred: VS Shell installation has failed with exit ...
Jonathan Allen's user avatar
169 votes
13 answers

How can I move a database from one server to another?

How can I move MySQL tables from one physical server to another? Such as this exact scenario: I have a MySQL server that uses innodb table and is about 20GB size. I want to move it to a new server, ...
John's user avatar
  • 1,851
167 votes
5 answers

How to list all constraints of a table in PostgreSQL?

How to list all constraints (Primary key, check, unique mutual exclusive, ..) of a table in PostgreSQL?
Thirumal's user avatar
  • 2,468
158 votes
9 answers

How to properly format sqlite shell output?

If I go to mysql shell and type SELECT * FROM users I get - +--------+----------------+---------------------------------+----------+-----------+--------------------+--------------------+ | USERID | ...
Kshitiz Sharma's user avatar
158 votes
12 answers

How do I move SQL Server database files?

I have a database and want to move the .mdf and .ldf files to another location. But I do not want to stop the MSSQLSERVER service, and I do not want to export to another server. How can I do this?
user avatar
157 votes
3 answers

PostgreSQL multi-column unique constraint and NULL values

I have a table like the following: create table my_table ( id int8 not null, id_A int8 not null, id_B int8 not null, id_C int8 null, constraint pk_my_table primary key (id), ...
Manuel Leduc's user avatar
  • 1,681
149 votes
4 answers

Is it safe to delete mysql-bin files?

I have MM Replication in mysql, and I want to squeeze some free space in the box be deleting unnecessary files, I came across these mysql-bin files inside /var/db/mysql/ There are hundreds of those ...
user avatar
148 votes
4 answers

Optimizing queries on a range of timestamps (two columns)

I use PostgreSQL 9.1 on Ubuntu 12.04. I need to select records inside a range of time: my table time_limits has two timestamp fields and one integer property. There are additional columns in my ...
Stephane Rolland's user avatar
148 votes
3 answers

Advantages and Disadvantages to using ENUM vs Integer types?

Lets say in some random table, you have a column named status. It's real-world values would be either enabled or disabled. Is it better for this column's data type to be an int/bool (1 or zero) or to ...
Jake Wilson's user avatar
  • 2,447
146 votes
11 answers

How to easily convert utf8 tables to utf8mb4 in MySQL 5.5

I have a database which now needs to support 4 byte characters (Chinese). Luckily I already have MySQL 5.5 in production. So I would just like to make all collations which are utf8_bin to utf8mb4_bin....
geoaxis's user avatar
  • 1,797
146 votes
8 answers

Pattern matching with LIKE, SIMILAR TO or regular expressions

I had to write a simple query where I go looking for people's name that start with a B or a D: SELECT FROM spelers s WHERE LIKE 'B%' OR LIKE 'D%' ORDER BY 1 I was wondering if ...
Lucas Kauffman's user avatar
145 votes
8 answers

Why shouldn't we allow NULLs?

I remember reading this one article about database design and I also remember it said you should have field properties of NOT NULL. I don't remember why this was the case though. All I can seem to ...
Thomas Stringer's user avatar
145 votes
3 answers

How can I specify the position for a new column in PostgreSQL?

If I have a table with the columns: id | name | created_date and would like to add a column, I use: alter table my_table add column email varchar(255) Then the column is added after the ...
Jonas's user avatar
  • 33.3k
143 votes
15 answers

PostgreSQL not running on Mac

The error in its entirety reads: psql: could not connect to server: No such file or directory. Is the server running locally and accepting connections on Unix domain socket "/tmp/.s.PGSQL.5432"?...
Michael P.'s user avatar
  • 2,101
143 votes
7 answers

How to use psql with no password prompt?

I wrote a script to REINDEX indexes in a database. Here is one of them: echo -e "\nreindex for unq_vbvdata_vehicle started at: `date "+%F %T"`" >> ${LOG_FILE} psql -U ${USERNAME} -h ${HOSTNAME} ...
Majid Azimi's user avatar
  • 2,281
143 votes
1 answer

Postgres UPDATE ... LIMIT 1

I have a Postgres database which contains details on clusters of servers, such as server status ('active', 'standby' etc). Active servers at any time may need to fail over to a standby, and I don't ...
vastlysuperiorman's user avatar
142 votes
5 answers

Possible to make MySQL use more than one core?

I've been presented with some dedicated MySQL servers that never use more than a single core. I'm more developer than DBA for MySQL so need some help Setup The servers are quite hefty with an OLAP/...
gbn's user avatar
  • 70k
140 votes
8 answers

How to turn JSON array into Postgres array?

I have a column data of type json that holds JSON documents like this: { "name": "foo", "tags": ["foo", "bar"] } I would like to turn the nested tags array into a concatenated string ('foo, ...
Christoph's user avatar
  • 1,593
137 votes
5 answers

Measure the size of a PostgreSQL table row

I have a PostgreSQL table. select * is very slow whereas select id is nice and quick. I think it may be that the size of the row is very large and it's taking a while to transport, or it may be some ...
Joe's user avatar
  • 1,645

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